The present invention relates to a power unit for a saddle type vehicle. More particularly, the invention relates to improvements in a power unit for driving the front wheels and the rear wheels of a saddle type vehicle which includes a crankshaft of an engine, a main shaft, a secondary shaft and an output shaft of a transmission, and a casing joined to the lower end of the cylinder block of the engine and supporting the crankshaft. The main shaft, the secondary shaft and the output shaft are disposed in parallel to the longitudinal axis of the vehicle and positioned below a saddle type seat. 2. Description of Background Art
A power unit of the aforesaid type is disclosed in, for example, Japanese Patent Publication (Kokoku) No. 63-46250.
When the main shaft, the secondary shaft and the output shaft extend in parallel to the crankshaft disposed longitudinally of the vehicle as mentioned above, the transmission gears may be spur gears and the front driving shaft and the rear driving shaft for driving the front wheels and the rear wheels, respectively, can be coupled directly with the secondary shaft or the output shaft, which is advantageous to the simplification of the construction of the power unit and the improvement of the transmission efficiency.
As described in the aforesaid Japanese patent publication, the crankshaft, the main shaft, the secondary shaft and the output shaft are arranged on substantially the same level, the rear end of the secondary shaft is connected to the rear driving shaft, and the front end of the output shaft is connected to the front driving shaft. The output shaft is driven synchronously through a chain by the secondary shaft. The casing of this power unit can be formed in a comparatively flat shape having a small height, the overall height of the power unit is small and the center of gravity can be lowered. On the other hand, since the shafts are arranged laterally of the vehicle, the casing has a comparatively large width and, inevitably, the space between the right and the left step is increased.